In a number of areas of the world there is a problem associated with the production of fluids such as crude oil from a subterranean geologic formation or reservoir which is referred to in the oil patch as "sand control". Sand control means preventing or otherwise alleviating the buildup of particles in the producing wellbore. This particle buildup is caused by settling of the particles out of the produced fluids (oil, water, etc.) when those fluids reach the wellbore itself. Although the term "sand control" is used, it should be understood that the problem particles involved are not limited to sand grains, but can include other solid particles, such as clay particles, that are entrained in the fluids produced from the formation through the wellbore wall into the wellbore itself. Sand control can be a substantial problem when the produced fluids flow from an unconsolidated formation or even from a consolidated, but uncemented, formation.
Solid particle buildup occurs in a wellbore or one or more regions thereof depending upon the completion configuration of the well, e.g., wells completed so as to produce from two or more formations. The problem particles settle out of the produced fluids when those fluids enter the wellbore because the velocity of the produced fluids is reduced in the wellbore as compared to the interstitial velocities of those fluids within the formation matrix itself. This is particularly true in areas near the wellbore wall itself.
A conventional technique used to control sand (solid particle) buildup in producing wellbores is to underream the wellbore, i.e., enlarge the diameter of the wellbore in the area in which the produced fluids enter the wellbore from the formation, insert a slotted liner in the underreamed portion of the wellbore, the slotted liner being sized so as to allow an annular region between the liner and the wellbore wall, and disposing a solid subdivided material such as gravel in the annulus between the liner and the wellbore wall. This way, as produced fluid passes through the gravel pack into the interior of the slotted liner for production to the earth's surface, the gravel pack serves as a filter medium to help remove some of the entrained particles from the produced fluid passing there-through.
Another sand control technique conventionally used is to case the wellbore with metal casing in the fluid producing zone, pertorating the casing, and then pumping a slurry containing gravel or the like into the formation around the perforated casing.
Sand buildup within the wellbore can occur even when a gravel pack or other filtering medium is employed in the wellbore since the gravel pack's efficiency is selective with regard to particle size. Often, even though larger particles are trapped by the gravel pack, substantial amounts of smaller particles pass through the pack and settle out in the interior of the wellbore itself thus creating a sand control problem in spite of the presence of a gravel pack.